<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        span {
            width: 20px;
        }

        .flex {
            width: 40px;
            height: 40px;
            display: flex;
            /* flex-direction: row; */
            /* flex-direction: row-reverse; */
            /* flex-direction: column; */
            /* flex-direction: column-reverse; */

            /** default 不换行 */
            /* flex-wrap: nowrap; */
            /* 换行，第一行在上方 */
            /* flex-wrap: wrap; */
            /* 换行，第一行在下方。 */
            /* flex-wrap: wrap-reverse; */

            /* 项目在主轴上的对齐方式 */
            /* justify-content: flex-start; */
            justify-content: flex-end;
            /* justify-content: center; */
            /* justify-content: space-between; */
            /* justify-content: space-around; */


        }
    </style>
</head>

<body>

    <div class="flex">
        <span>1</span>
        <span>2</span>
        <span>3</span>

    </div>

</body>

</html>